In recent years, vehicles driven by electric power have been used.
This leads to a need for supplying electric power to a vehicle.
For example, electric power is supplied to a parked vehicle by an electric power supply apparatus.
The electric power supply apparatus is capable of supplying electric power to a vehicle wirelessly.
For example, such an idea has been studied that a vehicle has a wireless type electric power supply secondary coil on a bottom part thereof, and an electric power supply primary coil is provided below the vehicle to supply electric power to the vehicle.
FIGS. 6A and 6B are conceptual diagrams of a wireless power transfer system.
The concept illustrated in FIGS. 6A and 6B has been disclosed in U.S. Pat. No. 8,035,255.
When the wireless type power transfer is employed, it is desired that electric power is supplied with a small energy loss from the electric power supply primary coil to the electric power supply secondary coil.
Furthermore, when the wireless type power transfer is employed to supply electric power from the electric power supply primary coil to the electric power supply secondary coil, it is desired that usage is easy.
In the wireless power transfer system, electric power is supplied wirelessly from the electric power supply primary coil to the electric power supply secondary coil via a magnetic field formed in a space between the electric power supply primary coil and the electric power supply secondary coil.
This feature imposes a reasonable restriction on a distance and a misalignment between the electric power supply primary coil and the electric power supply secondary coil. An attempt to supply electric power while exceeding the restriction of distance and misalignment leads to failure, that is, a large energy loss.